Humans want to believe that they're the smartest creatures on the planet. But the more we understand octopuses, the more it seems that we may not be alone in our ability to solve problems, make complex connections between ideas, and survive by wits alone. A growing body of evidence — a lot of it still anecdotal — suggests that octopuses show elements of human-like intelligence. But their intelligence has evolved for very different reasons than ours did, which makes them particularly difficult to understand.

Over at Orion magazine, Sy Montgomery has an incredible, in-depth article about what it's like to know octopuses (we linked to it a few weeks ago) — and perhaps, what it's like to be one. He interviews scientists who work with these invertebrates, and eventually befriends an octopus named Athena. Here's a fascinating piece of his article, which you will definitely want to read in full at Orion:

Octopuses have the largest brains of any invertebrate. Athena's is the size of a walnut-as big as the brain of the famous African gray parrot, Alex, who learned to use more than one hundred spoken words meaningfully. That's proportionally bigger than the brains of most of the largest dinosaurs.

Another measure of intelligence: you can count neurons. The common octopus has about 130 million of them in its brain. A human has 100 billion. But this is where things get weird. Three-fifths of an octopus's neurons are not in the brain; they're in its arms.

"It is as if each arm has a mind of its own," says Peter Godfrey-Smith, a diver, professor of philosophy at the Graduate Center of the City University of New York, and an admirer of octopuses. For example, researchers who cut off an octopus's arm (which the octopus can regrow) discovered that not only does the arm crawl away on its own, but if the arm meets a food item, it seizes it-and tries to pass it to where the mouth would be if the arm were still connected to its body.

"Meeting an octopus," writes Godfrey-Smith, "is like meeting an intelligent alien." Their intelligence sometimes even involves changing colors and shapes. One video online shows a mimic octopus alternately morphing into a flatfish, several sea snakes, and a lionfish by changing color, altering the texture of its skin, and shifting the position of its body. Another video shows an octopus materializing from a clump of algae. Its skin exactly matches the algae from which it seems to bloom-until it swims away.

For its color palette, the octopus uses three layers of three different types of cells near the skin's surface. The deepest layer passively reflects background light. The topmost may contain the colors yellow, red, brown, and black. The middle layer shows an array of glittering blues, greens, and golds. But how does an octopus decide what animal to mimic, what colors to turn? Scientists have no idea, especially given that octopuses are likely colorblind.

But new evidence suggests a breathtaking possibility. Woods Hole Marine Biological Laboratory and University of Washington researchers found that the skin of the cuttlefish Sepia officinalis, a color-changing cousin of octopuses, contains gene sequences usually expressed only in the light-sensing retina of the eye. In other words, cephalopods-octopuses, cuttlefish, and squid-may be able to see with their skin.

Though octopuses may sense the world very differently than we do, researcher Jennifer Mather has also witnessed surprisingly human behavior. Montgomery writes:

One octopus Mather was watching had just returned home and was cleaning the front of the den with its arms. Then, suddenly, it left the den, crawled a meter away, picked up one particular rock and placed the rock in front of the den. Two minutes later, the octopus ventured forth to select a second rock. Then it chose a third. Attaching suckers to all the rocks, the octopus carried the load home, slid through the den opening, and carefully arranged the three objects in front. Then it went to sleep. What the octopus was thinking seemed obvious: "Three rocks are enough. Good night!"

The scene has stayed with Mather. The octopus "must have had some concept," she said, "of what it wanted to make itself feel safe enough to go to sleep." And the octopus knew how to get what it wanted: by employing foresight, planning-and perhaps even tool use.

In the book Octopus: The Ocean's Intelligent Invertebrate, Mather and her colleagues take you through the lifecycle of octopuses, creatures who are still poorly understood. Much of our observations of octopus reproduction, for example, come from one female octopus who decided — oddly — to lay her eggs in a popular diving area near Seattle. Tucked into a den she created beneath a sunken boat, she spent almost a year tending her eggs. The entire time, she was observed daily by divers, many of whom interacted with her and gave her food. One group of those divers took careful notes of their observations to hand off to Mather and her team.

From these citizen scientists in diving gear, scientists learned females tending eggs soon stop eating — spending as much as 200 days starving themselves while they carefully blow water across their eggs and caress them to keep them clean and healthy. The octopus, nicknamed Olive by the divers, eventually saw the births of thousands of her young — only to die a few days later. Octopuses live only about three years, though there may be some deep sea species that can live for a decade.

Montgomery suggests that part of what makes octopus intelligence so alien to us is their short lifespans. But also, perhaps more importantly, they are non-social:

The octopus mind and the human mind probably evolved for different reasons. Humans-like other vertebrates whose intelligence we recognize (parrots, elephants, and whales)-are long-lived, social beings. Most scientists agree that an important event that drove the flowering of our intelligence was when our ancestors began to live in social groups. Decoding and developing the many subtle relationships among our fellows, and keeping track of these changing relationships over the course of the many decades of a typical human lifespan, was surely a major force shaping our minds.

But octopuses are neither long-lived nor social. Athena, to my sorrow, may live only a few more months-the natural lifespan of a giant Pacific octopus is only three years. If the aquarium added another octopus to her tank, one might eat the other. Except to mate, most octopuses have little to do with others of their kind.

So why is the octopus so intelligent? What is its mind for? Mather thinks she has the answer. She believes the event driving the octopus toward intelligence was the loss of the ancestral shell.

Predators who crave squishy-bodied octopus treats would exert strong selection pressure. Only the smartest octopuses would survive — the ones who could hide the most cunningly, traveling alone to avoid exposure.

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It's becoming clear that octopuses use tools to hide all the time. After all, an octopus will gather stones to camouflage the entrance to its den. When Olive made her nest near Seattle, she built a small wall of stones around the entrance, almost like she was creating a courtyard.

Given the different origins and functions of our intelligences, it's likely that octopuses find humans as perplexing as we find them. You can imagine an octopus saying to a human, "Why the hell are you always trying to hang out with me? Don't you know that socializing leads to death?" At the same time, we may seem weirdly noncommunicative to an octopus, given that our bodies always stay the same shape and color. They might even dismiss us as incapable of intelligent discussion.

The question for octopus researchers, then, might be how to communicate with creatures whose minds are optimized for hiding and solitude. Perhaps we'll have to change our definition of intelligence before we finally realize we discovered non-human intelligent life long ago.